Radiation curable resin, paint or ink vehicle composition comprising said resin and magnetic recording medium or resistor element using said resin

ABSTRACT

A resin having a monomer unit structure represented by the formula: ##STR1## can be cured by an actinic irradiation such as electron beam, ultraviolet ray or infrared ray to give a heat-resistant, moisture-resistant, acid- and alkali-resistant and solvent-resistant film which is especially suitable for a paint vehicle resin for use in resistor element or magnetic recording medium. A composition comprising said resin modified by incorporating at least of one monomer or oligomer containing at least one acryl, methacryl or allyl group therein for facilitating the control of the characteristics of a resistor element obtained by using said composition is also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to a radiation curable resin, a paint orink vehicle composition comprising said resin, a conductive or magneticpaint or ink comprising said vehicle composition, a resistor elementusing said conductive paint or ink and a magnetic recording medium usingsaid magnetic paint or ink in a dried state. 2. Description of the PriorArt:

A number of resins, which can be cured by ultraviolet ray, electron beamor the like, have recently been developed and are now commerciallyavailable. Compared with the conventional thermo-setting resins, theseradiation curable resins harden in an extremely short time and exhibitexcellent properties and therefore are in wide use.

However, since many of these resins are esters such as acrylates,methacrylates, allylates and the like, they have poor alkali-resistantand poor solvent-resistant properties compared with usual thermo-settingresins to limit the scope of their application. In addition to this,they have problem of poor heat-resistant property.

Furthermore, these resins are, in general, inferior in their surfacehardness, to a phenolic resin or the like which has an excellent surfacehardness. In the case wherein the resins are modified to intentionallybe increased of their surface hardness, their adhesive property andflexibility would be decreased. Moreover, since the low molecular weightcompounds are used, they have drawback in their poor leveling propertywhen they are incorporated into paint. In contrast to this, the phenolicresin has a drawback that it requires a long curing time.

A carbon-resin composition type resistor element has been widely used asa fixed resistor or a variable resistor. Since the conventional resistorelement of this type utilizes a thermo-setting resin as its binderresin, a process at high temperature and a long time is required for itsmanufacturing. Moreover, if the resistor element is laminated on a paperlaminated phenolic sheet or the like, there has been a problem that adegradation of the substrate occurs during the thermo-setting processand an improvement therefore has long been awaited.

SUMMARY OF THE INVENTION

It is therefore the primary object of the present invention to provide aresin which can be cured in a short time by the irradiation ofultraviolet ray, electron beam or the like. The resin is purposed tohave an excellent surface hardness and at the same time a good adhesiveproperty, and to have remarkable heat-resistant and solvent-resistantproperties which had not been observed with the conventional radiationcurable resins. It is another object of the present invention to providea paint or ink vehicle composition comprising said radiation curableresin as such, said resin and at least one of monomers or oligomer, saidresin modifying dispersing properties of ferromagnetic powder orconductive powder.

It is further object of the present invention to provide a conductive ormagnetic ink or paint comprising said vehicle composition and saidferromagnetic powder or conductive powder.

It is still another object of the present invention to provide aresistor element which has solved the above-described problems inherentto the manufacturing process of the conventional carbon-resincomposition type resistor element.

Other objects and attendant advantages of the present invention will bemade apparent to those skilled in the art by reading the followingdetailed description of the invention and attached claim.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1(a) and 2 are infrared absorption spectra of the radiationcurable resins manufactured in accordance with the present invention,and

FIG. 1(b) is an infrared absorption spectrum of an intermediate obtainedin the manufacturing process of said resin.

DETAILED DESCRIPTION OF THE INVENTION

A radiation curable resin of the present invention is characterized tohave a monomer unit structure represented by the formula: ##STR2##wherein, R is methylol group, acrylated or methacrylated methylol group,and the molar ratio of the methylol group to the acrylated ormethacrylated methylol group is preferably in the range of from 20:1 to1:3.

In the case wherein said molar ratio is more than 20:1, namely theamount of the methylol group is too much, the radiation curable propertyof the resin becomes poor and too much energy would be required for thecuring. In contrast to this, if said molar ratio is less than 1:3,namely the amount of the methylol is too small, an effect ofpolymerization attributable to the condensation of the methylol groupbecomes small and, as the result, the effective improvement of the resinin its solvent-resistant and heat-resistant properties, being the objectof the present invention, would be made unduly small.

The resin having a monomer unit structure of the present invention maybe prepared by allowing tetramethylol bisphenol A(tetrahydroxymethylbisphenol A), obtained by a reaction of one mole ofbisphenol A with four moles of formaldehyde in a basic solution, toreact with acrylic acid, methacrylic acid or a lower alcohol esterthereof. The condensation product of bisphenol A and formaldehyde hasbeen known. The present inventors have found that, by esterifying themethylol group in the above-mentioned condensation product with acrylicacid or methacrylic acid, a radiation curable resin having an excellentradiation curable property, a high surface hardness, an excellentadherence property and a good leveling property can be obtained.

The radiation curable resin prepared in accordance with the presentinvention can be cured by the irradiation of ultraviolet ray, infraredray or electron beam in a short time to give a coated film of smooth andhigh surface hardness. The resin of the present invention can also beused in paint for magnetic recording media with remarkable advantage inthe dispersion of ferromagnetic powder.

Incidentally, the resistor element in accordance with the presentinvention is characterized in the use of the above-mentioned resin,namely, the acrylic acid or methacrylic acid ester of the bisphenolA-formaldehyde condensation product, or in the use of a mixture composedof said ester and a monomer or oligomer containing at least one acryl,methacryl or allyl group therein, or the both, as the binder resin.

The conductive ink can be prepared by dispersing the conventionallyknown conductive powder such as metal powder, carbon black or graphitein the binder resin and by adding solvent therein if desired. Theresistor element of excellent characteristics can be prepared in a shorttime by applying the above-mentioned ink on a substrate, drying, ifdesired, and irradiating, electron beam or infrared ray by means of aradiation type heater for a short time.

As the monomer or oligomer to be mixed with the above-mentioned ester,those having at least one acryl, methacryl or allyl group therein may beexemplified. These monomers or oligomers may be mixed with the esterindividually but two or more of the monomers and oligomers may be usedtogether in a mixture system. In most cases, the use of the mixturesystem facilitates the control of the characteristics of the obtainedresistor element.

The available monomer or oligomer may be exemplified as acrylates ofprimary or polyhydric alcohol or oligoacrylates such as methyl acrylate,ethyl acrylate, propyl acrylate, butyl acrylate, hydroxyethyl acrylate,2-ethylhexyl acrylate, ethylene glycol diacrylate, trimethylolpropanetriacrylate, pentaerythritol triacrylate, epoxy acrylates, oligoesteracrylates, urethane acrylates or the like. They may further beexemplified as methacrylates of primary or polyhydric alcohol such asmethyl methacrylate, ethyl methacrylate, propyl methacrylate, butylmethacrylate, hydroxyethyl methacrylate, 2-ethylhexyl methacrylate,diethylene glycol dimethacrylate, trimethylolpropane trimethacrylate orthe like, or allyl alcohol, diallyl ether, diallyl adipate, diallylphthalate, both end diallylates of low molecular weight polyurethane orthe like.

The mixing ratio of the acrylate or methacrylate solution of thebisphenol A-formaldehyde condensation product to the above-mentionedmonomer or oligomer can arbitrarily be selected in compliance with thecharacteristics required for the resistor element.

As the conductive powder to be dispersed in the resin composition, anyof the known conventional ones may be used. They can be exemplified asmetal powders of silver, copper or the alloy thereof, metal oxidespowder, metal carbides powder, metal nitrides powder, metal boridespowder, carbon black, graphite, mixtures thereof or the like. The mixingratio of the conductive powder to the above-mentioned binder resincomposition may be in the conventionally known range. The binder resincomposition and the conductive powder may be mixed with optionaladdition of solvent and dispersed thoroughly in a known manner to give aconductive ink. This conductive ink may be painted on a substrate andirradiated by electron beam after drying if desired, or irradiated bymeans of radiation type heater to give a resistor element.

The obtained resistor element is extremely hard and is particularlysuited for the resistor element used in a variable resistor whichrequires a good abrasion resistant property.

In manufacturing magnetic recording media, such as magnetic tape ormagnetic disk, the previously described radiation curable resin of thisinvention may also be used with advantages in view of its excellentadherence property to the substrate and good abrasion resistant propertyof the coated surface. Particularly advantageous feature of the resin isin its excellent ability of dispersing the ferromagnetic powder whichwill be demonstrated in the description of preferred embodiment below.

In this case also, the resin may be combined with at least one of theabove-mentioned monomer or oligomer as has been described with respectto the resistor element.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description, the present invention will be elucidatedin more detail by way of example.

EXAMPLE 1

Bisphenol A (1 mole) and 38% formaldehyde solution (4.5 moles) wereplaced in a four-necked flask equipped with a thermometer, a stirrer, areflux condenser and a dropping funnel, and a 6 N aqueous solution ofsodium hydroxide (2.2 moles) was dropped therein through the droppingfunnel while the temperature of the reaction mixture was kept under 60°C. After the dropping was finished, the mixture was allowed to react at60°±1° C. for 2 hours. The reaction mixture was then neutralized with 6N sulfuric acid aqueous solution and washed with water. It wasthereafter condensed under reduced pressure to give an 85% solutionconsisting mainly of tetramethylol bisphenol A. Nine (9) parts by weightof this solution was then combined with 1 part by weight of n-propanoland 7 parts by weight of isophorone to be dissolved completely andthereafter 8 parts by weight of acrylic acid and 0.02 part by weight ofp-toluene sulfonic acid were added therein. The mixture was allowed toreact at 60°±1° C. for 6 hours under the reduced pressure by means ofaspirator. After the reaction, the mixture was cooled down to 40° C. andthe unreacted acrylic acid was removed off under reduced pressure togive 20 part by weight of an ester solution.

An infrared absorption spectrum of the resultant resin is shown in FIG.1(a) and that of the intermediate, tetramethylolbisphenol A is shown inFIG. 1(b). From the ratios of the absorbance at 1485 cm⁻¹ attributableto the benzene ring and absorbance at 1405 cm⁻¹ attributable to thevinyl group, it was confirmed that the resin of this example contains2.2 moles of acryl ester for the previously described monomer unit.

To the obtained solution, there was added benzoine ethyl ether (ethylbenzoate) of an amount equivalent to 2% for the solid resin componentand the mixture was applied to an alumina substrate using a doctor bladeof 25μ and dried. This was then irradiated by means of high pressuremercury lamp of 120 W/cm placed at a distance of 10 cm for 30 seconds.The obtained film was very smooth and hard showing a pencil hardness of6H. Soaking of this film in molten solder at 350° C. for 10 secondsresulted in a little browning but no peeling off of the film from thesubstrate or no crack of the film itself was occurred. Furthermore, nochange was observed with this film after being washed in an ultrasonictrichloroethylene bath. In this example, an extention of the ultravioletirradiation to 1 minute raised the surface pencil hardness to 8H. For acomparison, a molten solder soaking test at 350° C. of an ultravioletcured product of commercially available polyepoxyacrylate containing 2%of ethyl benzoate was performed. As a result, the resin was decomposedto evolve a gas. An ultrasonic washing of a commercially availableproduct in trichloroethylene resulted in decrease in surface hardness ofthe product.

Next, the obtained solution was applied to an iron plate in thethickness of 50μ and dried, and then irradiated by an electron beam of165 KeV in 10 M rad to give a hard film of a pencil hardness of 7H. Apost-curing of this film at 190° C. for 5 minutes gave it a pencilhardness of 9H.

EXAMPLE 2

The reaction time for the esterification in the process described inExample 1 was extended to 15 hours to give a result that the content ofthe acryl ester in said monomer unit reached 3 moles for the monomerunit. This resin was cured in a similar manner as described in Example 1to acquire a pencil hardness of 5H by the ultraviolet irradiation for 15seconds. A molten solder soaking test of this product at 350° C. showeda slight foaming.

EXAMPLE 3

A process similar to that described in Example 1 was performed. In thiscase, however, the amount of the acrylic acid added at the preparationof the acryl ester was 4 parts by weight and the reaction time was 2hours. As a result, a conversion rate of the methylol group to theacrylate ester was 0.05 mole for the monomer unit. An absorptionattributable to condensation of methylol group was observed around 1650cm⁻¹. This resin gave a coated film having a pencil hardness of 4H by anultraviolet irradiation for 30 seconds. A coated film having a pencilhardness of 7H was obtained by irradiating the resin using an electronbeam of 165 KeV in 50 M rad. A post-curing of this film at 190° C. for 5minutes gave it a surface a pencil hardness of 9H.

EXAMPLE 4

A process similar to that described in Example 1 was performed. In thiscase, however, 8.5 parts by weight of methacrylic acid was used in lieuof the acrylic acid and the reaction mixture was allowed to react at60°±1° C. for 6 hours to give 2.2 parts by weight of a resin solutioncontaining 2.4 moles of methacryl ester. The content of the ester wasdetermined by the ratios of the absorbance of benzene ring at 1490 cm⁻¹to that of vinyl group at 1295 cm⁻¹. An infrared absorption spectrum ofthis resin is shown in FIG. 2.

Ethyl benzoate (benzoine ethyl ether) was added to the obtained solutionin the amount of 2% for the solid resin and the mixture was applied toan alumina substrate and dried. A coated film having a pencil hardnessof 7H was obtained by irradiating ultraviolet ray for 30 sec. No peelingoff or cracking was observed with this film at a molten solder soakingtest at 350° C.

Next, the solution was applied to an iron plate and dried, and thenirradiated by an electron beam of 165 KeV in 10 M rad to give a hardcoated film having a pencil hardness of 8H. The pencil hardness of thisfilm was raised to 9H or more by post-curing at 190° C. for 5 minutes.

A coated film obtained by applying this solution to a paper laminatedphenolic sheet, drying and electron beam irradiating also showed apencil hardness of 8H and an adhesive property of 100% at "cellophantape peeling test".

EXAMPLE 5

A process similar to that described in Example 4 was performed. In thiscase, however, the amount of the methacrylic acid added was 10 parts byweight and the reaction time was 15 hours, and a resin containing 3moles of methacryl ester for a monomer unit was obtained. This productgave a coated film having a pencil hardness of 5H by an ultraviolet rayirradiation for 15 seconds which showed no peeling off or cracking in amolten solder soaking test at 350° C.

EXAMPLE 6

A process similar to that described in Example 4 was performed. In thiscase, however, the amount of the added methacrylic acid was 5 parts byweight and the reaction time was 2 hours to give a resin containing 0.05mole of methacryl ester for a monomer unit. Like in the case of Example3, an absorption attributable to the condensation of methylol group wasobserved around 1650 cm⁻¹. This resin also gave a coated film having apencil hardness of 5H by an ultraviolet irradiation for 30 seconds. Anelectron beam irradiation in 50 M rad resuls in a coated film having apencil hardness of 7H. A post-curing of this film at 190° C. for 5minutes raised its pencil hardness to 9H or more.

EXAMPLE 7

The solution obtained in a process of Example 1 was combined with asolution of a commercially available urethane acrylate (mean molecularweight; about 30,000) in 1:1 ratio of the solid resin components. To themixture, there was added ethyl benzoate (benzoin ethyl ether) in theamount of 2% for the solid component and the resultant mixture wasapplied to a film (75μ) of polyethylene terephthalate and dried. Theresin was cured by irradiating ultraviolet ray for 15 seconds. Thecoated film was clear and smooth, and having a pencil hardness of 5H. Nopeeling off or cracking was occurred in a folding test of 180° around acylinder of 3 cm diameter.

EXAMPLE 8

A mixed solution obtained in Example 7 (containing no ethyl benzoate)was combined with commercially available γ-iron oxide powder (needlessof 0.3 μm length) and fine powder of carbon, and the combined mixturewas milled in a pot mill to give a magnetic ink. As a result offiltration of this ink through a filter paper performed in order toexamine the extent of dispersion, the whole amount was able to befiltered out. In contrast to this, as a result of filtration of amagnetic ink which did not contain the resin prepared in accordance withthe present invention but did contain only urethane acrylate resin, itwas found that about 50-70% of the powder was remained on the filterpaper. From this experiment, it was confirmed that the radiation curableresin of the present invention was suited for dispersing the magneticpowder.

EXAMPLE 9

A white ink was prepared by mixing the solution, obtained in accordancewith Example 1, with alumina powder of the amount equivalent to thesolid component in the solution and titanium dioxide of 1/10 weight ofthe solid component followed by a milling by a three-roll mill. The inkwas applied to an iron plate, dried, and then irradiated by an electronbeam of 165 keV at 10 M rad (for 1 second or less) to give a coatedfilm. The film surface was smooth and showed a pencil hardness of 9H ormore, and the film showed an excellent adhesion property to the ironplate.

EXAMPLE 10

(a) Preparation of acryl ester solution of bisphenol A-formaldehydecondensate:

Bisphenol A (1 mole) and 38% formalin (4.5 moles) were placed in afour-necked flask equipped with a thermometer, a stirrer, a refluxcondenser and a dropping funnel and a 6 N aqueous solution of sodiumhydroxide (2.2 moles) was dropped therein through the dropping funnelwhile the temperature of the reaction mixture was kept under 60° C.After the dropping was finished, the mixture was allowed to react at60°±1° C. for 2 hours. The reacted mixture was then neutralized with 6 Nsulfuric acid aqueous solution and washed with water. Thereafter, it wascondensed under reduced pressure to give an 85% solution consistingmainly of tetramethylolbisphenol A.

A hundred (100) parts by weight of this solution was then mixed with 50parts by weight of isophorone and the mixture was removed of residualmoisture under reduced pressure. To the resultant mixture, there wereadded 70 parts by weight of acrylic acid containing 4000 ppm ofhydroquinone and 0.2 part by weight of p-toluene sulfonic acid. Themixture was then allowed to react at 80°±1° C. for 1 hour and theunreacted acrylic acid was removed off under reduced pressure.Thereafter, a 60% solution was prepared by adding ethanol.

(b) Resistance ink:

A resistance ink was prepared by adding 15 g of carbon fine powder and30 g of butyl Carbitol to 50 g of the solution obtained in the above (a)and by milling the mixture with a three-roll mill.

(c) Resistor:

A resistor was prepared by applying the above-described resistance inkto a paper laminated phenolic sheet, drying and then irradiating anelectron beam of 165 KeV at 15 M rad thereon. The time required for theelectron beam irradiation was 0.1 second or less for the length of 15cm. The resultant resistor was a hard one having a pencil hardness of 8Hand an area resistance of 0.5 kΩ/□. This resistor was subjected to aheat-resistant test at 85° C. and a moisture-resistant test of 95% R.H.at 60° C. to give the resistance changes of -3.0% and 1.0%, respectivelyafter 1000 hours. As a result of a rotation test performed on a variableresistor assembled with this resistor element, it was confirmed that noabnormality in noise or the like was observed with this resistor after30,000 rotations. For a comparison, a heat-resistant test and amoisture-resistant test were performed on a resistor prepared by using aresistance ink of thermo-setting type resin. As the result, theresistance changes of -5.5% and 2.5% were observed, respectively.

EXAMPLE 11

A process similar to that described in Example 10 was performed. In thiscase, however, 35 parts by weight of methacrylic acid was used in lieuof the 70 parts by weight of acrylic acid and the removal of theresidual monomer was omitted. The obtained resistor element had an arearesistance of 0.7 kΩ/□ and a pencil hardness of 9H or more, and showedthe resistance changes of -3.0% and 1.0%, respectively, after theheat-resistant and moisture-resistant tests.

EXAMPLE 12

A process similar to that described in Example 10 was performed. In thiscase, however, 3 g of trimethylolpropane trimethacrylate and 30 g ofepoxy acrylate (Viscoat #540, available from Osaka Yuki Kagaku K. K.)were used in addition to 50 g of acryl ester condensate solution as thebinder resin, and the amount of carbon fine powder was 30 g. Theobtained resistor element had area resistance of 0.6 kΩ/□ and a pencilhardness of 7H and showed the resistance changes of -9.5% and -1.5%,respectively, after the heat-resistant and moisture-resistant tests.

EXAMPLE 13

A process similar to that described in Example 12 was performed. In thiscase, however, 18 g of oligoester acrylate (Aromix M-8030, availablefrom Toa Gosei K .K.) and 6 g of hexanediol diacrylate were used inaddition to 50 g of acryl ester condensate solution as the binder resin.The obtained resistor element had area resistance of 1 kg/□ and a pencilhardness of 9H, and showed, after the heat-resistant andmoisture-resistant tests, the resistance changes of -8.5% and 2.5%,respectively.

EXAMPLE 14

A process similar to that described in Example 10 was performed. In thiscase, however, 5 g of diethyleneglycol dimethacrylate was added to 50 gof ester condensate solution as the binder resin to give a resistorelement having an area resistance of 0.5 kΩ/□ and a pencil hardness of9H or more. This resistor element showed, after the heat-resistant andmoisture-resistant tests, the resistance changes of -2.5% and 1.5%,respectively.

EXAMPLE 15

A process similar to that described in Example 12 was performed. In thiscase, however, 20 g of diallyl orthophthalate prepolymer and 10 g ofpentaerythritol triacrylate were used in addition to 50 g of acryl estercondensate solution as the binder resin to give a resistor elementhaving an area resistance of 1 kg/□ and a pencil hardness of 9H or more.This resistor element showed, after the heat-resistant andmoisture-resistant tests, the resistance changes of -8.0% and 1.5%,respectively.

EXAMPLE 16

A resistor element was prepared by applying the resistance ink obtainedin the process of Example 10 on a paper laminated phenolic sheet andirradiating the applied substrate by long wave infrared radiationequipment of 1.8 kW output. The distance between the radiator and thesubstrate was 10 cm. The obtained resistor element had an arearesistance of 0.6 kΩ/□ and a pencil hardness of 9H or more. It showed,after the heat-resistant and moisture-resistant tests, the resistancechanges of -3.5% and 1.2%, respectively.

What is claimed is:
 1. A radiation curable resin which comprises apolymeric tetramethylol bisphenol derivative having a monomer unitstructure represented by the formula: ##STR3## wherein R is a mehtylolgroup, and acrylated or methacrylated methylol group, and th molar ratioof the methylol group to the acrylated or metharcrylated methylol groupis in the range of 20:1 to 1:3.